The naturally occurring magnesium borate mineral, Mg₃B₇O₁₃Cl, is characterized by a rigid
framework of B-O bonds together with a regular void structure, ideally forming crystals in the
face-centered cubic structure and characterized by the space group F-43c (#219). Recently,
several structurally related Li ion conducting boracites and thioboracites have been synthesized
and computationally investigated, including Li₄B₇O₁₂Cl [1], Li₄Al₃B₄O₁₂Cl [2], and Li₆B₇S₁₃I [3].
The high ionic conductivity of all of these materials is related to the occurrence of natural
interstitial Li sites due to the high symmetry of the crystalline structures. In this presentation, we
report the results of computational analysis and simulations of the large family of Li₄ and Li₆
ion-conducting boracites and thioboracites, including the experimentally identified materials and
several computationally predicted materials. The simulation results provide guidance on the
detailed mechanisms of Li ion mobility, the stability of materials with respect to decomposition,
and the structural stability of the materials with respect to rhombohedral and other distortions.

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[1] Y. Li and N. A. W. Holzwarth, Phys. Rev. Materials 6, 025401 (2022)
https://doi.org/10.1103/PhysRevMaterials.6.025401.
[2] K. Kajihara, N. Tezuka, M. Shoji, J. Wakasugi, H. Munakata, and K. Kanamura, Bulletin of
the Chemical Society of Japan 90, 1279 (2017) https://doi.org/10.1246/bcsj.20170242.
[3] K. Kaup, K. Bishop, A. Assoud, J. Liu, and L. F. Nazar, J. Am. Chem. Soc. 143, 6952 (2021)
https://doi.org/10.1021/jacs.1c00941.

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The work was supported by NSF Grant No. DMR-1940324. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the university.